Acoustic shocks are sounds of the hissing type composed of one or more frequency components that may appear during the reproduction of a multimedia audio stream (speech, music, sound) and the mean level of which may be lower than the mean level of the useful digital audio signal and may go as far as saturation of the digital audio signal. Even at very low levels, acoustic shocks have a not insignificant impact on health (psychophysiological effects) in particular when they occur on telephone services, and more particularly in a call centre.
It is easy to detect acoustic shocks during periods of silence but it becomes difficult when the shock is at a low level and is added to speech or music.
Known protection techniques are based either on temporal (envelope) approaches and on the detection of signals with an excessively high energy, or on a finer analysis of the time-frequency type. In the first case, it is impossible to discriminate a speech signal from a shock, and even to detect a low-energy shock, especially when it is mixed in another signal (speech for example). In the second case, the detection is based on a calculation of physical parameters and on threshold values associated with these physical parameters. The previous techniques are still not very robust, in particular to the problem of detecting a mixed shock. The result is either numerous false alarms (detection of shock where there is only speech), and strong degradation of said speech, or non-detections, which no longer provides protection for the user.
The prior art knows, through the American patent application no 2005/0105717, a telephone interface system. This American patent application of the prior art describes a system for protection against acoustic shocks. This system is composed of several stages. There are in particular limiters, compressors, noise reducers and a module that detects and suppresses shocks of the pure sound type. This system affords, by means of a time/frequency analysis, detection of acoustic shocks. Nevertheless, its action is limited to a single frequency per band between [0-2300] and [2300-4000] Hz. In addition, the peak-detection algorithm remains dependent on the volume. Finally, in order to be able to detect all the shocks, the detection criterion as proposed in this American patent application of the prior art gives rise to numerous false detections over periods of speech. These excessively numerous false detections give rise to filtering of certain useful components of the speech signal, which impacts on the voice quality.